Urokinase is a new drug for dissolving blood clots which has been shown to be effective in treating pulmonary emboli and will probably become available to American physicians within the next several years. Urokinase may be useful in the treatment of an eye disease known as central retinal vein occlusion. Patients with this disease usually have only one eye affected, but more than 90 percent of affected eyes will incur significant visual loss, and as many as 30 percent of these eyes may develop painful secondary glaucoma and eventually require surgical removal. Because treatment with urokinase exposes the patient to some risk of bleeding complications, this controlled, randomized clinical trial is being conducted to determine if the potential benefits to be gained from treatment of central retinal vein occlusion with urokinase justify the risk of this therapy.